Continuous Digester Inclined Separator Black Liquor Heating

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Solution Overview

Problem

Pulp digesters face production limitations due to high temperatures and low retention times, leading to increased reject levels and energy costs, especially when cool white liquor is introduced, which negatively impacts pulp quality and production.

Innovation Solution

A system and method to deliver impregnated lignocellulosic material to the digester at an elevated temperature using a pressurizable inclined top separator and black liquor circulation loop, allowing for efficient heating and separation of impregnated material while maintaining high temperature feed without excessive cooling media use.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If cool white liquor is introduced to the digester, then cooking temperature is reduced, but production level is negatively impacted

Engineering Contradiction:

Improvecooking temperatureVSAvoidproduction level

Core Design Contradiction:

TemperatureVSProductivity

Solution Approach 1:

The system divides the cooking process into two separate vessels: an impregnation vessel for chemical treatment and a digester for high-temperature cooking. This segmentation allows the impregnation vessel to operate at lower temperatures with cool white liquor while the digester maintains high production levels at elevated temperatures, resolving the contradiction between temperature control and productivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The impregnation vessel acts as an intermediary between chip preparation and the digester. It pre-treats chips with cooking chemicals at lower temperatures, then feeds the impregnated chips to the digester. This intermediary process allows cool white liquor to be used in impregnation without negatively impacting the high-temperature cooking and production levels in the digester.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Temperature

If impregnated chips are heated beforehand, then feed temperature is maintained, but energy cost increases

Engineering Contradiction:

Improvefeed temperatureVSAvoidenergy cost

Core Design Contradiction:

TemperatureVSUse of energy by moving object

Solution Approach 1:

The system merges the heating function into the digester vessel rather than requiring separate pre-heating equipment. The digester's heating system directly heats the impregnated chips upon entry, eliminating the need for separate pre-heating steps and reducing overall energy costs while maintaining high feed temperature for efficient cooking.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The digester serves dual functions: it both cooks the impregnated chips and provides the necessary heating. The system uses the digester's own heating capacity and retained heat to maintain feed temperature, making the system self-sufficient and reducing external energy requirements compared to separate pre-heating systems.

Inventive Principle:

Principle #25Self-service

3Productivity

If digester is run at production limits, then productivity is maximized, but reject levels increase

Engineering Contradiction:

Improveproduction levelVSAvoidpulp quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The impregnation vessel performs preliminary chemical treatment of chips before they enter the digester. This pre-impregnation with cooking chemicals ensures uniform chemical distribution and proper preparation, which maintains pulp quality and reduces reject levels even when the digester operates at maximum production capacity with high temperatures and short retention times.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach enhances pulp cooking uniformity, reduces reject levels, lowers bleaching chemical consumption, and achieves lower operating costs while maintaining production levels in an energy-efficient manner.

Implementation Method 1

a black liquor circulation and heating loop including a warm black liquor inlet in communication with said warm black liquor outlet, a heater for heating warm black liquor to produce hot black liquor

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

a pressurizable, inclined top separator including a sluicing liquor inlet for receiving a sluicing mixture comprising impregnated lignocellulosic material and sluicing liquor

Methodology Applied

Scientific EffectGravity separation: Gravitation

Data Source

PatentEP3224408B1Continuous digester and feeding system

Publication Date: 2018.11.21 INT PAPER CO

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AI summary

One embodiment provides an apparatus for cooking lignocellulosic material, comprising a pressurizable, inclined top separator including a sluicing liquor inlet for receiving a sluicing mixture comprising impregnated lignocellulosic material and sluicing liquor, a hot black liquor inlet, an excess liquor outlet, and an impregnated lignocellulosic material outlet; a continuous digester vessel including an impregnated lignocellulosic material inlet in communication with the impregnated lignocellulosic material outlet, and a warm black liquor outlet; and a black liquor circulation and heating loop including a warm black liquor inlet in communication with said warm black liquor outlet, a heater for heating warm black liquor to produce hot black liquor, and a hot black liquor outlet in communication with said hot black liquor inlet. Methods of making and using the apparatus are also provided.